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The objective of this study is to demonstrate the use of subcritical steam to pretreat coal for slurry liquefaction, allowing liquefaction to be carried out at lower severity and improving product yield and quality. Samples of Illinois No. 6 coal were pretreated in 750 psia steam at 340{degree}C for 15 minutes. These samples, as well as raw coal, were liquefied at high (400{degree}C, 30 min.) and low (385{degree}C, 15 min.) severity conditions under 1500 psia hydrogen with tetralin as the donor solvent. Improved yields were obtained at both conditions. (Improved yields were not obtained at a liquefaction temperature of 350{degree}C as that put the sample into the region of retrogressive reactions). The deleterious effects of slow heating and exposure of the sample to air were demonstrated. Under low severity conditions, steam pretreatment more that doubled the oil yield, increasing it from 12.5 to 29 wt %. Tests were also conducted with aromatic ethers as model compounds. These were exposed to inert gas and steam at pretreatment conditions and in some cases to liquid water at 315{degree}C. {alpha}-Benzylnaphthyl ether and {alpha}- naphthylmethyl phenyl ether show little difference in conversion and product distribution when the thermolysis atmosphere is changed from inert gas to steam. However when these compounds were reacted in the presence of 5 {angstrom} zeolite, the yields of the thermolysis products improved. Zeolite proved effective in suppressing isomerization of the starting materials. These results suggested that zeolites might be beneficial in steam pretreatment of coal and in coal liquefaction. Pretreatment and liquefaction of mixtures of coal and zeolites increases yields of asphaltenes and preasphaltenes

Steam pretreatment for coal liquefaction. Final report, September 26, 1990--March 18, 1995